Ductile iron is a cast iron comprising spheroidal graphite, with which large-dimensioned parts can be mass-produced economically. For example, the housing of a steam turbine is conventionally manufactured from ductile iron. The geometrical dimensions of a steam turbine in the upper power range, as are used for example for generating electricity in steam power plants, are however so large that problems can occur when casting ductile iron. For example, there is a high likelihood that nonuniformities and defects will occur in such a steam turbine housing, which compromise the strength of the steam turbine housing. Depending on the position in the part and the function of the positions affected, these nonuniformities and defects may be intolerable. There is therefore an upper limit on the maximum permissible size of housing parts made of ductile iron. A remedy would be provided by a housing part which is composed of a plurality of small pieces that are not critical in terms of casting technology. A prerequisite for this, however, would be that these pieces can form a housing when welded together. The pieces would need to be connected to one another by means of large-area welded connections, for which a suitable welding method would be necessary. However, no manufacturing method is known by which these types of large-area welded connections of ductile iron can be produced.
In general, nonuniformities and defects always occur in cast parts produced from ductile iron. The size and position of the nonuniformities and defects dictate whether the cast part in question must be discarded as a reject. For small local defects, repair welding methods are known. Such a repair welding method is, for example, cold welding with an iron-nickel alloy. However, the cold welding method produces a welded connection whose strength is less than the strength of the ductile iron. The cold welding method is therefore unsuitable for large-area welded connections. Another method is hot welding, although this can only be carried out by preheating of the part in the range of from 500° C. to 600° C., and subsequent heat re-treatment. Hot welding is therefore very complicated and generates distortion of the part, so that hot welding is unsuitable for large-area connection welding of ductile iron.